1. Field of the Invention
The invention relates to a process, for preparing alkylchlorosilanes which may include hydrogen, in the presence of an alumina catalyst which proceeds continuously in a moving bed reactor.
2. Description of the Related Art
The preparation of alkylchlorosilanes by direct synthesis (Müller-Rochow synthesis) results, apart from the main dialkyldichlorosilane product, in further silanes such as tetraalkylsilane, trialkylchlorosilane, and alkyltrichlorosilane inter alia, for which there is varying demand and, in the event of a surplus, a possible use is required. In the distillation of the crude silane mixture from the direct synthesis of alkylchlorosilanes and chlorosilanes, first runnings and intermediate fractions are also obtained, which cannot be utilized directly for further processing.
For instance, it is well known from the literature that aluminum chloride in all forms catalyzes the rearrangement of alkyl chlorosilanes, even on support materials such as aluminas. These are processes in fixed bed reactors. In US20030109735, the conversion in the trimethylsilane+methyltrichlorosilane or trimethylchloro-silane+methyltrichlorosilane reactions is improved by adding magnesium oxide, for example, to the aluminum chloride. DE 2351258 describes the addition of promoters to such reactions, these minimizing the discharge of aluminum chloride from the reaction vessel. U.S. Pat. No. 6,175,029, in contrast, describes the use of very pure alumina as a catalyst. EP 0146148 also describes the use of zeolites as a catalyst for the rearrangements. DE 102008043331 describes the improvement of the conversion level in a fixed bed reactor through an addition of magnesium, copper or zinc in the alumina.
Fixed bed reactors have the disadvantage that the catalyst exchange becomes ever more technically demanding with increasing reactor size. An environmentally friendly emptying operation requires a deactivation, for example, in order to prevent outgassing of silanes and hydrogen chloride as a result of hydrolysis or ingress of air. Equally, some silanes having hydrogen on the silicon self-ignite on ingress of air. The refilling of a shell and tube reactor in particular is complicated by the fact that all the tubes have to have the same pressure differential to assure optimal catalyst exploitation.